Monitoring heparin therapya role for the chromogenic assay

: Heparin therapy was evaluated by simultaneous determinations of the activated partial thromboplastin time (APTT), and plasma heparin levels by chromogenic assay. These tests showed good correlation (r = 0.73) in patients on heparin alone. However, in the presence of concurrent warfarin administration, r fell to 0.37, reflecting an additional warfarin effect upon the APTT. Furthermore, the studies confirmed the increased heparin requirement in patients with pulmonary embolization.